The best cellphone I ever had was long like an energy bar gray Siemens, rectangular one, like 1x2 inch, about 4.5 inch long, in 1999, in South Africa. It was GSM then over there, and all telephony was digital. Sound quality was very good. Car kits were required. All of them were wired, no blue teeth, just jack plugs. No echo, no intermittent loss of signals, and there was an option to see on display which cell station it is connected to currently.

I guess I'm going to have to read more on this. From what I know, both AM and FM modulation produces sidebands of equal amplitude. Given normal instruments, there is no easy way to see if the lower sideband is 180° out of phase with the upper sideband.

We do know that pure AM modulation will give you a carrier and two sidebands, and that's it. FM modulation will generate increasing sidebands as you increase the level of modulation. This may be the best way to determine whether you are dealing with an AM or FM issue. Only very low deviation FM modulation will generate one carrier and two sidebands.

I guess I'm going to have to read more on this. From what I know, both AM and FM modulation produces sidebands of equal amplitude. Given normal instruments, there is no easy way to see if the lower sideband is 180° out of phase with the upper sideband.

We do know that pure AM modulation will give you a carrier and two sidebands, and that's it. FM modulation will generate increasing sidebands as you increase the level of modulation. This may be the best way to determine whether you are dealing with an AM or FM issue. Only very low deviation FM modulation will generate one carrier and two sidebands.

Can we expect wide deviation from an opamp?
I don't think so. That means, we can't see more than one pair of strips generated such a way.
But since both AM and FM present, their lower sidebands will be out of phase, upper sidebands in phase, and as the result we'll have higher upper sideband than lower one. This would be the chance to prove presence of PIM.

My method is to push the topology into the direction to highlight the phenomenon in question. How? To conduct series of experiments with different phase parameters, and added non-linearities, then see the whole picture in dynamics.

As the result of experiments I know what to do in order to minimize the phenomenon in question.

Here is one way to avoid PIM generated by a MOSFET with feedback: to use feedback in phase with it's own non-linear capacitances, so errors and feedback would be aligned in phase, and no PIM generated by feedback:

I think that Matti first mistook the added pips to be the 2F2-NF1 series, because the 2F2-9F1 seemed to fit fairly closely. It is just that some of them DON'T fit closely enough. It was just the wrong path to take, but all pioneers go up 'blind alleys' some of the time. Everyone, please understand that.

Please note folks, the basics are still not agreed on. John, as Gerhard showed ALL the tones are EXACTLY on NF1+-MF2.

__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Hi Scott,
That's exactly what my earlier line of questioning to John was all about. With no targets in sight, we're simply spinning our wheels. At least with a verified test circuit, we can see what comes out, therefore confirming or disproving any previous statements in that direction. From what I've read and understand so far, this distortion effect seems to be in a special case. Only when the amplifier in question has been driven to the point where it's gain starts to compress will any trouble come about. That's assuming that the amplifier will suffer gain droop at high output levels before gross distortion sets in.

Hi Anatoliy,
We both agree that the actual amount of this particular distortion created is very likely to be a very small amount. So small in fact that sidebands may not appear above the noise floor for starters. The entire argument is really premature until we have a sense of magnitude. I suspect that all you may see is AM modulation in nature, the FM contribution being so small.

Quote:

Can we expect wide deviation from an opamp?

I don't understand where you are going with this to begin with. I do not expect a large amount of PIM or TIM from any amplifier, chip or otherwise. As I mentioned, I intend to read more information on this before making a factual statement of any kind. I think I want to run the experiment myself to see what the result actually is.

Quote:

But since both AM and FM present, their lower sidebands will be out of phase, upper sidebands in phase, and as the result we'll have higher upper sideband than lower one.

You really lost me here Anatoliy. Each sideband will be displaced from the center frequency by the same amount - the frequency of the modulating signal. The amplitudes will be the same as an absolute value, we can't see the phase when using a spectrum analyzer.

Quote:

My method is to push the topology into the direction to highlight the phenomenon in question. How? To conduct series of experiments with different phase parameters, and added non-linearities, then see the whole picture in dynamics.

What topology are you talking about?
So how is your testing method different from anybody else? It seems to be the natural way to test.

Quote:

As the result of experiments I know what to do in order to minimize the phenomenon in question.

Well, why else do the experiment? Mind you, the mechanism may not be so obvious. You may well find out that this particular thing is not of any concern as well.

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to use feedback in phase with it's own non-linear capacitances, so errors and feedback would be aligned in phase, and no PIM generated by feedback:

I see a current generated feedback voltage in your diagram. Besides, I don't think anyone has said that PIM is created in the feedback loop. I understand that the issue exists in the forward amplification path.

Quote:

Where else should they be, if no DSP involved?

Didn't this experiment take place before DSP was in significant use? In other words, I don't think John and company used any DSP techniques. Therefore, we are not concerned with DSP in any way unless you want to use these methods to uncover the distortion products. In that case, it's doubtful that anyone on that team saw any PIM or TIM.

You know, the first time I saw the acronym "TIM" applied to distortion, I found it to be pretty amusing. Why? Well, because "TIM" stands for Technician Induced Malfunction. Now, that's pretty funny if this turns out to be an error in test method!

You really lost me here Anatoliy. Each sideband will be displaced from the center frequency by the same amount - the frequency of the modulating signal. The amplitudes will be the same as an absolute value, we can't see the phase when using a spectrum analyzer.

Chris; if you are talking of PIM you've lost AIM. If you are talking of AIM you've lost PIM. If PIM is generated by non-linearity that means AIM must already present, so if you sum their products you will get asymmetrical specter. It is well known in radio fact, and let me repeat again, it is the method of generating SSB signals well known in radio, one of basic things.

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What topology are you talking about?
So how is your testing method different from anybody else? It seems to be the natural way to test.

Any topology. Did you read the paper Jan Didden posted?

Quote:

I see a current generated feedback voltage in your diagram. Besides, I don't think anyone has said that PIM is created in the feedback loop. I understand that the issue exists in the forward amplification path.

It exists in both; but M. Otala's and J Curl's paper deals with PIM generated by an amp with no PIM, but with a phase lag, when a negative feedback is applied. "Fixing" non-linear distortions it creates PIM, as stated in that paper.

I don't understand where you are going with this to begin with. I do not expect a large amount of PIM or TIM from any amplifier, chip or otherwise. As I mentioned, I intend to read more information on this before making a factual statement of any kind. I think I want to run the experiment myself to see what the result actually is.

You really lost me here Anatoliy. Each sideband will be displaced from the center frequency by the same amount - the frequency of the modulating signal. The amplitudes will be the same as an absolute value, we can't see the phase when using a spectrum analyzer.

-Chris

Hi Chris,

Anatoliy is correct about the sidebands being of unequal amplitude if both am and fm at the same modulating frequency are present. I believe I also mentioned this several posts ago. Because the upper and lower sideband phase relationships are different for am and small-deviation fm, the sidebands will augment each other on one side and fight each other on the other side.

On another note, I do expect a lot of TIM and PIM from some amplifiers under some conditions. The 741 on which Fig. 3 was based is a very good example. That op amp is being crushed, and all kinds of bad things are happening.

Matti was probably right to choose that amplifier to make clear what he was talking about, but that is not a good example upon which to base a high-end audio discussion.

Matti was probably right to choose that amplifier to make clear what he was talking about, but that is not a good example upon which to base a high-end audio discussion.

Yes, but in order to understand where is the right direction sometimes it is good to see an opposite side, since errors are visible to everyone, but clean reproduction may be questioned by some who expect specific sound to be reproduced. For example, my wife did not object sounds from mass production systems until she realized at once how close reproduction may be to real sounds. The same happens to other people who don't hear the direction to clearness, but hears well distortions, and sees them on spectrum analyzer screens. Show them the wrong direction, and they would not object the opposite way. However, I have to admit that there are more of wrong ways, but the single right one.